1. Field of the Invention
The present disclosure relates to a fixing apparatus that is mounted in an image forming apparatus, such as an electrophotographic copying machine, a printer, or the like.
2. Description of the Related Art
A fixing apparatus mounted in an image forming apparatus, such as an electrophotographic copying machine, a printer, or the like typically adopts a heat fixing method in which a toner is melted by heat and is fixed on a recording material. In recent years, as one form of the heat fixing method, an electromagnetic induction heating fixing apparatus has been developed to practical use. The electromagnetic induction heating fixing apparatus has an advantage in that the warming-up time needed to raise the temperature to a temperature that enables fixing to be carried out is short.
Japanese Patent Laid-Open No. 2014-026267 discloses an electromagnetic induction heating fixing apparatus having a small thickness and little restriction in material quality of a conductive layer of a heat generating roller (a heat generating belt) that is a heat generating rotating member.
Typically, an electromagnetic induction heating fixing apparatus guides the lines of magnetic force that are generated by a coil into a desired shape with a magnetic member (a magnetic core). Ferromagnetic ceramics, such as ferrite, is typically used for the magnetic core. Since ceramics such as ferrite is formed using a mold, as the size becomes larger, it becomes harder to achieve precision and fabrication thereof becomes more difficult, and, consequently, the magnetic core becomes costly. Accordingly, a configuration that uses and arranges a plurality of small magnetic cores is typically employed.
Incidentally, in a fixing apparatus in which a helical-shaped coil is used and in which magnetic cores are disposed inside the coil, when there are gaps between the cores, the heat generation amount at each position corresponding to the gap decreases and the heat distribution of the heat generating roller becomes disadvantageously uneven. It has become known that the gaps between the magnetic cores have a large influence on the heat distribution particularly in devices with a shape such as the device disclosed in Japanese Patent Laid-Open No. 2014-026267 in which most of the lines of magnetic force that exit an end portion of the magnetic cores pass outside the heat generating roller and return to the other end of the magnetic cores. When the heat distribution becomes uneven, the quality of the image after fixing becomes degraded.